.item{
    float: left;
    width: 25%;
    height: 260px;
    background-repeat: no-repeat;
    background-position: center;
    background-size: cover;
}
/* pad  1080 */
@media screen  and  (max-width:1080px){
    .item{ width: 50%;}
}
/* 手机 640 */
@media screen  and  (max-width:640px){
    .item{ width: 100%;}
}

// ======================================
.item{
    float: left;
    width: 25%;
    height: 260px;
    background-repeat: no-repeat;
    background-position: center;
    background-size: cover;
    @media screen and  (max-width:1080px) {
        width: 50%;
    }
    @media screen  and  (max-width:640px){
        width: 50%;
    }
}

